This invention relates to medical diagnostic imaging systems, and more particularly, to apparatus and methods for providing a highly versatile diagnostic medical imaging system capable of performing a plurality of different penetrating radiation imaging examinations, including radiographic, fluoroscopic, tomographic, and stepped radiographic/fluoroscopic examinations.
A wide spectrum of equipment is now commercially available for performing diagnostic medical imaging examinations using penetrating radiation or electromagnetic fields. Although there is great diversity in complexity, application, and cost, among the available commercial products, a significant problem for many users of diagnostic imaging equipment is the lack of a general-purpose, highly versatile platform for efficiently conducting a variety of different types of examinations while producing high quality results.
There are, for example, several fairly recently developed imaging modalities (such as Magnetic Resonance Imaging, Computed Tomography, Positron Emission Tomography, etc.), which provide images of high diagnostic quality. However, these devices rely on elaborate arrays of mechanical equipment, radiation or field detectors, and computers and signal processors, and therefore, they are expensive to purchase and operate. This expense is reflected in the fees charged to patients, either directly or indirectly, when they are examined. As a result, although these newer imaging modalities may be generally useful, there is substantial pressure on health care providers to order such examinations only when conventional imaging modalities cannot be used. This class of imaging equipment has therefore become highly specialized because each system is narrowly directed to a single imaging modality, and because their high cost prevents their general application to run-of-the-mill imaging.
Other relatively specialized equipment has been developed to accomplish more conventional imaging examinations. Fluoroscope systems often lack facilities for conventional radiographic examinations. Conventional linear tomography systems typically have mechanical couplings between an X-ray source and a film holder or other image receiver, and these couplings may make it difficult to use such systems for general purpose radiography. Even when multiple purpose imaging systems have been provided in the past, it has been relatively difficult and time consuming to convert such systems from one imaging mode to another. This undesirably decreases the flexibility of the imaging system, and increases the cost of examinations provided thereby.
Another problem to which the present application is directed is providing high quality peripheral angiography examinations. Peripheral angiography is a diagnostic roentgenographic procedure providing visualization and recording of the blood vessels in the peripheral region of the body, such as the arms and legs. In a typical peripheral angiography examination, a radiopaque contrast agent is injected into a blood vessel, and a rapid sequence of radiographs are taken to observe the progress of the contrast agent as it flows through the vessels along the length of the extremity. The contrast agent is initially concentrated in the blood vessels and takes some time to diffuse generally into the surrounding regions. Thus, the contrast agent renders the blood vessels visible under radiography provided that the radiographs are taken very soon after the contrast agent arrives in a particular region. In conventional Peripheral Angiography examinations, the patient is supported on a movable table top positioned under system control, The table top, in turn, is supported by a stationary radiographic-fluoroscopic table. An overhead X-ray source (which may be mounted on a tube crane) directs a beam through the patient to a "rapid film changer" device.
The locations of interest at any particular time during the examination are in the general vicinity of the leading edge of the contrast material as it progresses though the extremity. In conventional peripheral angiography systems, the rapid film changer is normally in a fixed position. Because the length of the recording radiographic film or imaging device is not sufficient to cover the entire extremity, conventional peripheral angiography systems require that the patient be rapidly repositioned throughout the procedure to fully visualize and record the contrast material as it progresses through the vessels of the extremity (i.e., the patient must be rapidly repositioned throughout the procedure to maintain the contrast material within in the field of view of the rapid film changer). In such conventional systems, the patient rests on a movable table-top, which may travel as rapidly as 9 in/sec between exposures.
Conventional peripheral angiography systems exhibit several disadvantages which reduce the quality of the examinations provided thereby. The position and stability of the patient during the exposure which produces an angiogram is very critical. Even slight movement of the patient contributes to film blur and reduces the diagnostic quality of the examination. The above-mentioned conventional equipment moves the table top supporting the patient very rapidly between exposures. This adds to patient discomfort and may cause motion artifacts.
Another disadvantage of conventional peripheral angiography examination systems is that the typical image recording apparatus (a rapid film changer) is not adapted for automatic exposure controls. The exposure "technique" (that is, exposure parameters such as exposure time and X-ray tube voltage and current) is vital to the success of a peripheral angiography examination. It is often desirable to conduct a study of the entire leg of a patient. Since some portions of the leg are substantially thicker than others, the exposure parameters must be modified during the examination. As a result, the operator must accurately predict and preset the exposure parameters required for each examination step. Although some operators perform a test exposure before injecting the contrast agent, the contrast agent itself varies the radiographic density of the region under study, and it is difficult to adjust in advance the exposure parameters to compensate for this.
For useful results, a peripheral angiography examination requires perfect coordination and timing. Following the injection of the contrast medium, there is only a very short interval in which to maneuver the necessary equipment into place, adjust controls, and change the exposure factors. For example, in some examinations a delay of even one second in making the exposure may render the projection valueless. The operator must calculate in advance the rate of injection, and the speed of the contrast medium flow, and must select in advance the number of steps to be taken, their positions, and the time to progress the next step. Thus, a further disadvantage of conventional peripheral angiography examination systems is that such systems require the operator to plan the coordination of each step in advance, and the systems provide little assistance to the operator. The usual method of assuring that a complete examination will be performed is to perform plural overlapping exposures. This undesirably increases the radiation does received by the patient, and drives up the cost and time required for the examination.
Another disadvantage of the conventional peripheral angiography examination equipment is that the rapid film changer is placed in a fixed position under the table top. Therefore, the table cannot be tilted as is desirable to control the gravitational flow of the contrast medium.